The distribution of audio and video (“AV”) content in motor vehicles is an emerging market. The manufacturing of modern motor vehicles has included such features as rear seat entertainment systems which can display high-definition formats to vehicle occupants. These entertainment systems allow for an occupant to view navigational data as well as watch broadcast or cinematic programming. An occupant can watch commercially available content on entertainment systems from connected electronic devices, including blu-ray players, which can display various formats such as 1080p to the viewer. Connecting an entertainment system to a high definition device, such as blu-ray player, requires a suitable connection, which can support the transmission of the uncompressed digital data.
The transmission of high definition content, in particular high definition content on commercially distributed materials, is regulated in an effort to prevent piracy of the materials. Encryption of the high definition content transmitted from the commercial materials allows for the prevention of unlawful distribution of those commercial materials. Content encrypted from the materials cannot be freely copied and distributed. Digital copyright protection systems prevent a copyrighted work from displaying on a device that does not support the copyright protection system. For the transmission of high definition content, the standard used is known as high-bandwidth digital copyright protection (“HDCP”). Manufacturers who wish to display high definition content on their device, may obtain a license that unlocks and allows the high definition content to display on the device. HDCP restricts the transmission of HDCP encrypted content and prevents that content from playing on an unlicensed device that does not support HDCP.
One significant characteristic of the HDCP 1.X standard (including HDCP standards 1.0 and 1.4), is that while it allows for the transmission of the encrypted content, it does not allow the transmission to be of a ‘broadcast’ type. HDCP 1.X supported device transmitters must connect to each respective HDCP receiver via a point-to-point link. If more than one audio/video receiver (display) is to be connected to a transmitter, a HDCP repeater must be implemented. This repeater consists of a HDCP receiver which decrypts the audio/video content and a set of one or more transmitters which re-encrypt and transmit the audio/video content again. This breaks the tree structure of a broadcast system into a set of point-to-point links. The HDCP repeaters at the tree nodes are expensive to implement. They typically include a microcontroller subsystem running software to handle the communication between upstream and downstream point-to-point links. In some applications (e.g. the automotive case) it may be highly undesirable to have a need for ‘intelligent’ nodes at remote locations of an audio/video distribution network. Instead, there is a strong desire to centralize all software execution in one spot, typically at the top of the audio/video distribution tree where a powerful processor already resides.
A point-to-point link can be establish to separately connect each of the individual rear display monitors directly to the transmitter, as illustrated in FIG. 1. In FIG. 1, each of the cables can be driven by its own built-in encryption engine 12, 14, and 16, in transmitter 10, and each of the displays monitors 20, 30, and 40 can separately decrypt the HDCP encrypted content through decryption engines 22, 32, and 42, to display the content on the individual display monitor. However, the usage of separate individual cables to accomplish the transmission to multiple receivers or display monitors creates additional weight in the vehicle, and is not cost effective to implement.
One way to overcome the need for separate point-to-point connection cables is to merge the unencrypted audio/video streams into a single unified stream. The single stream is then encrypted resulting in a single unified encryption stream (“UES”). The UES is transmitted to a receiver which decrypts the entire UES before separating the UES into individual audio/video streams. Because decryption occurs for the entire UES instead of the individual audio/video streams, a single set of keys are used to encrypt and decrypt all of the audio/video streams, and the audio/video streams are protected by one set of encryption and decryption engines.
A system using a daisy chain topology for transmitting a UES is illustrated in FIG. 2. In motor vehicle design, using a daisy chain to connect multiple outputs devices to a transmitter is preferable because it drastically reduces the amount of cable used, and subsequently the cost and weight of the cable. The displays, as depicted in FIG. 2, are connected in a daisy chaining fashion. In transmitter 110, multiple audio/video streams are combined in an adder and fed to encrypter 112, where encrypter 112 encrypts the combined stream into a UES and sends the UES via a cable to the first of the receivers. The first receiver 120 receives the UES and decrypts it via a decryption engine 122. One of the audio/video streams is displayed on the display 125 in receiver 120. The UES is sent through HDCP repeater 123 and re-encrypted through encrypter 124 and transmitted from the first receiver to a subsequent display or receiver. At the second receiver 130, the UES is decrypted by decryption engine 132 and one of the audio/video streams is displayed locally at display 135. The UES may again be encrypted by encryption engine 134 and transmitted to a subsequent display or receiver. This process is repeated for the remaining display monitors.
The described daisy-chain of displays depicted in FIG. 2, must use HDCP Repeaters, such as repeater 123, in each daisy chain node. Since the primary audio/video sources and the transmitter must be aware of all connected audio/video sinks subsequently attached to it, a HDCP repeater must be employed to collect downstream information from a daisy chain connection and transmit it upstream towards the transmitter. Each intermediate node passes information of the subsequently connected downstream receivers or displays, topology, or public keys, back to the previously node, and eventually back to the audio/video source. This requires the presence of a microprocessor and a memory at each intermediate node, i.e display monitor or receiver. Implementing microprocessors and the corresponding software in each of the display units adds significantly to the cost and complexity of the overall of the system. The cost saved by reducing the cable length is outweighed by the additional cost of the additional microprocessors in each of the display monitors.
Implementing daisy chains to transmit the HDCP encrypted content can also be problematic in the event the encryption system fails. Because the streams have to be decrypted at each intermediate node, and re-encrypted for streams transmitted to subsequently connected display monitors or receivers, if the re-encryption of the streams fails at any of the nodes, all subsequently connected nodes will be affected. Therefore, the failure of the encryption engine at any of the connected display monitors prevents the decryption and display of the remaining audio/video streams at the subsequently connected display monitors or receivers.
Thus there remains a need in the art, for a cost effective architecture which allows for the daisy chaining of connected display monitors or receivers to a HDCP 1.X audio/video transmitter, without the use of HDCP repeaters on nodes of the intermediates nodes, which maximizes efficiency and minimizes area.